1. The Field of the Invention
The present invention relates generally to processes for upgrading low value by-products generated during petroleum refining. More particularly, the present invention relates to methods for increasing the mono-aromatic content of refining by-products that contain polynuclear aromatics, such as but not limited to cycle oils and pyrolysis fuel oil.
2. The Related Technology
Effective techniques for manufacturing the greatest amount of high quality products from low quality crudes are needed for the economic viability of the petroleum refining industry. Because crude oils are obtained from the ground, they can have widely varying types and amounts of hydrocarbons and impurities. Distillation of crude oils produces large fractions of hydrocarbons that are not very useful as fuels or other higher end uses. For decades, the refining industry has been intensively researching ways to economically convert these fractions into products that are more valuable. There are now many refining techniques that economically convert unusable fractions into higher value petroleum products.
Ideally all the hydrocarbons in a barrel of oil would be upgraded to high-value, useable products. However, despite the industry's extensive research there are certain by-products of the various refining processes that are difficult to upgrade. Difficult-to-upgrade hydrocarbons include pyrolysis fuel oil, which is a by-product of steam cracking to make olefins, and cycle oil, which is a by-product of fluidized catalytic crackers that are used extensively to produce gasoline stocks.
These hydrocarbons can be difficult to upgrade because they often contain impurities such as sulfur and heavy metals and/or significant quantities of very high molecular weight hydrocarbons, polynuclear aromatics, and asphaltenes. Hydrocarbons containing these types of hydrocarbons tend to form coke under hydrocracking conditions, which can foul reactors and reduce the yield of the hydrocracking process. Consequently, these products are often used “as is” in their low-value form.
Because pyrolysis fuel oil and cycle oil are a byproduct of important refining processes, these products are necessarily produced in most refineries and must be dealt with. The traditional approach has been to sell PFO and cycle oil as a fuel to be burned in power generation. PFO and cycle oils have a foul smell, are toxic, and produce pollution when burned. Environmental agencies have for years regulated the disposal and burning of PFO and cycle oils. These oils typically must be blended with other higher grade fuel oils to pass regulatory restrictions when burned. The restrictions make it even more difficult to use these materials as fuels and have suppressed the price that industry is willing to pay for them. Despite the continuing pressures to catalytically upgrade hydrocarbons such as PFO and cycle oil, thereby creating a long-felt but unsatisfied need, an economical process has thus far eluded the industry.